Best Spark Plugs For Ej25: Compare NGK Options by Fit

#1 · Best Overall

1. Sixity NGK Impreza Iridium

• Weight: 7.7 oz
• Dimensions: 5.83 x 4 x 1 in

Best for: Impreza 2.5L H4 replacement set.

Why it ranks #1: Its listing directly covers Impreza 2.5L H4 models across multiple years and supplies a four-pack of genuine NGK Iridium IX plugs.

The vehicle-specific 4-pack covers Subaru Impreza 2.5L H4 models from 2004 through 2014, giving owners a named application range instead of a generic plug listing. NGK Iridium IX construction and included hardware make this a direct-replacement option for buyers maintaining an Impreza within those listed years.

The compatibility listing names each Impreza model year from 2004 to 2014 and specifies the 2.5L H4, making the application unusually clear for owners of those cars. Four plugs arrive together, so the set suits a complete replacement rather than piecemeal purchasing. NGK Iridium IX plugs are identified as genuine NGK parts, and the included original packaging and hardware support a straightforward parts handoff during installation. The listing describes them as direct replacement auto parts.

Skip it if you own a WRX STI from 2013–2018; the Sixity Auto NGK Iridium IX WRX STI set lists that application.

Choose this set for a 2004–2014 Subaru Impreza with the listed 2.5L H4 when replacing all four plugs. Its vehicle range is specific, so other Subaru models and years fall outside the supplied fitment details.

Listed on Amazon as: 4 pc NGK Iridium IX Spark Plugs for Subaru Impreza 2.5L H4 2004-14

#2 · Impreza Ruthenium

2. Sixity NGK Impreza Ruthenium

• Weight: 7.7 oz
• Dimensions: 3.7 x 0.94 x 3.32 in

Best for: Impreza Ruthenium HX replacement.

Why it ranks #2: This four-pack specifically fits listed Impreza 2.5L H4 applications and uses NGK Ruthenium HX plugs.

NGK Ruthenium HX construction sets this four-pack apart, while its listing names Subaru Impreza 2.5L H4 models from 2004 through 2014. That combination gives owners within the stated range a vehicle-specific replacement option with a different NGK plug family than Iridium IX.

The stated compatibility covers Impreza model years 2004–2014 with a 2.5L H4, helping owners narrow the application to a named vehicle and engine. Four plugs are supplied as a set, and the listing identifies them as genuine NGK Ruthenium HX parts. It also describes the plugs as direct replacement auto parts and includes original packaging and hardware, supporting a complete replacement purchase without relying on loose, separately sourced components.

Skip it if you own a 2000–2012 Outback 2.5L H4; the Sixity Auto NGK Ruthenium HX Outback set lists that range.

For an Impreza 2.5L H4 from the listed 2004–2014 years, this Ruthenium HX four-pack pairs a named application with NGK parts and included hardware. Other models are not established by the supplied fitment.

Listed on Amazon as: 4 pc NGK Ruthenium HX Spark Plugs for Subaru Impreza 2.5L H4 2004-14

#3 · Outback Fit

3. Sixity NGK Outback Ruthenium

• Weight: 7.04 oz
• Core Material: Ruthenium

Best for: Outback Ruthenium HX set.

Why it ranks #3: The listing names Outback 2.5L H4 models across multiple years and specifies Ruthenium core material and a 0.04-inch gap.

This NGK Ruthenium HX four-pack lists Subaru Outback 2.5L H4 models from 2000 through 2012, making its vehicle range the key buying detail. Owners in that span get a named application, genuine NGK plugs, and included hardware in one direct-replacement set.

The fitment details enumerate Outback years 2000–2012 and specify the 2.5L H4, allowing owners to compare their vehicle against a stated application. The pack contains four NGK Ruthenium HX plugs and is described as genuine NGK direct replacement auto parts. Original packaging and hardware are included, keeping the replacement pieces together for installation. The 0.04-inch gap is also specified, a practical dimension to compare with the required plug specification.

Skip it if you service a 2004–2014 Impreza 2.5L H4; the Sixity Auto NGK Ruthenium HX Impreza set lists those model years.

This is the application-specific choice for an Outback 2.5L H4 within the listed 2000–2012 range. Its Ruthenium HX construction and four-plug pack suit a complete replacement, but the stated fitment is not broader.

Listed on Amazon as: 4 pc NGK Ruthenium HX Spark Plugs for Subaru Outback 2.5L H4 2000-12

#4 · WRX-Specific

4. Sixity NGK WRX Iridium

• Weight: 7.7 oz
• Dimensions: 5.83 x 4 x 1 in

Best for: WRX STI 2.5L H4 plug set.

Why it ranks #4: It is a four-pack of genuine NGK Iridium IX plugs listed for WRX STI 2.5L H4 models in a defined model-year range.

The listed 2013–2018 Subaru WRX STI 2.5L H4 application is this four-pack’s clearest advantage, helping owners shop by a specific model and engine rather than a broad Subaru category. NGK Iridium IX plugs, genuine NGK parts, and included hardware support a direct-replacement purchase for that stated range.

The compatibility details name WRX STI model years 2013 through 2018 and specify the 2.5L H4, giving owners a defined application to check against their car. Four plugs are supplied together for a full set replacement. The listing identifies the plugs as genuine NGK Iridium IX parts and calls them direct replacement auto parts; original packaging and hardware are included to keep the replacement components together for installation.

Skip it if you maintain a 2004–2014 Impreza 2.5L H4; the Sixity Auto NGK Iridium IX Impreza set lists those years.

This set suits WRX STI owners whose 2.5L H4 falls within the listed 2013–2018 range and who want four NGK plugs together. The supplied fitment does not establish compatibility with other Subaru models.

Listed on Amazon as: 4 pc NGK Iridium IX Spark Plugs for Subaru WRX STI 2.5L H4 2013-18

#5

5. Sixity NGK Baja G-Power

• Weight: 7 oz
• Dimensions: 3.31 x 0.94 x 3.32 in

Best for: 2003 Subaru Baja plug set.

Why it ranks #5: This four-pack is explicitly listed for the Baja 2.5L H4, but its application covers only one stated model year.

The listing names a 2003 Subaru Baja 2.5L H4 as the application for this four-pack of NGK G-Power plugs, giving Baja owners a precise vehicle reference. Genuine NGK parts, included hardware, and direct-replacement labeling round out the stated replacement details.

The specified application is a 2003 Subaru Baja with a 2.5L H4, so the listing gives owners a narrowly defined vehicle to compare against. Four NGK G-Power plugs arrive together for a complete set replacement. The product is identified as genuine NGK and as direct replacement auto parts, while included original packaging and hardware keep the replacement components together through the installation workflow.

Skip it if you maintain a 2004–2014 Impreza 2.5L H4; the Sixity Auto NGK Iridium IX Impreza set lists those years.

Choose this G-Power set for a 2003 Subaru Baja with the listed 2.5L H4 when replacing all four plugs. Its supplied fitment is narrowly specific and does not establish compatibility with other EJ25 vehicles.

Listed on Amazon as: 4 pc NGK G-Power Spark Plugs compatible with Subaru Baja 2.5L H4 2003

#6

6. NGK LKAR7BIX-11S

• Weight: 6.4 oz
• Core Material: Iridium

Best for: Anti-fouling feature prioritizers.

Why it ranks #6: The four-pack has Iridium IX construction and a listed 0.6-millimeter gap, but the supplied details do not identify an EJ25 vehicle fit.

NGK specifically cites superior anti-fouling for this Iridium IX plug, making its longer insulator nose a relevant feature for buyers prioritizing fouling resistance. The 0.6mm fine iridium tip and tapered ground electrode add defined ignition details, but no EJ25 vehicle fitment is provided.

The longer insulator nose is described as preventing fouling, while corrugated ribs are said to prevent flashover; these construction details give maintenance-minded buyers specific behavior to weigh. NGK also links the 0.6mm laser-welded iridium tip with a consistently stable spark and the tapered ground electrode with reduced electrical quenching. Four plugs come in the pack. Its M12 x 1.25 thread and 0.6mm gap are stated, not a Subaru application.

Skip it if you want listed EJ25 fitment; the Sixity Auto NGK Ruthenium HX Impreza set specifies 2004–2014 2.5L H4 models.

Choose this four-pack when its anti-fouling construction and M12 x 1.25 thread match your documented requirements. The supplied details do not name an EJ25, so it cannot establish vehicle fitment for this roundup.

Listed on Amazon as: NGK LKAR7BIX-11S Iridium IX Spark Plug (93501 Iridium Ix), 4 Pack

#7

7. NGK LKR7DIX-11S

• Weight: 6.4 oz
• Core Material: Iridium

Best for: Fine-tip ignition feature seekers.

Why it ranks #7: It includes four Iridium IX plugs with a listed 0.04-inch gap, though the product data does not specify Subaru or EJ25 compatibility.

Its 0.6mm laser-welded fine iridium tip is the defining feature, with NGK linking that construction to high durability and a consistently stable spark. A tapered ground electrode is also specified to minimize electrical quenching, though the listing does not identify an EJ25 vehicle application.

The fine iridium tip and tapered ground electrode address spark behavior: NGK says the tip provides a consistently stable spark while the electrode minimizes electrical quenching. A longer insulator with corrugated ribs is described as preventing flashover, and a triple gasket seal is intended to eliminate combustion gas leakage. Four plugs are included, but the listing’s 5/8-inch thread and 0.04-inch gap do not establish Subaru EJ25 fitment by themselves.

Skip it if you need explicit EJ25 fitment; the Sixity Auto NGK Impreza Iridium IX listing names 2004–2014 2.5L H4 models.

This four-pack fits buyers comparing its ignition and sealing features against a known plug specification. Its listed thread and gap are useful checks, but no EJ25 application is supplied, so fitment is unresolved.

Listed on Amazon as: NGK LKR7DIX-11S Iridium IX Spark Plug (93175 Iridium Ix), 4 Pack

#8

8. NGK CR9EIX

• Weight: 4.48 oz
• Core Material: Iridium

Best for: Iridium 10mm-thread plug buyers.

Why it ranks #8: This four-pack is a genuine NGK iridium plug, but its listed 10mm thread size and lack of EJ25 fitment detail leave compatibility unverified.

A 10mm thread size and iridium core distinguish this NGK CR9EIX four-pack, giving buyers concrete specifications to compare with an existing plug or application reference. The listing identifies it as an OEM NGK replacement part, but does not name an EJ25 or Subaru vehicle fitment.

The iridium core and top are specified alongside a 10mm thread size, which gives a buyer measurable details to compare with the required plug specification before purchase. NGK identifies the CR9EIX as a genuine OEM replacement part, and four plugs are included, supporting a matched set purchase. The listing says it is compatible with cars and trucks but does not identify Subaru models or EJ25 engines, so vehicle-specific confirmation remains essential.

Skip it if you need a listed Subaru application; the Sixity Auto NGK Impreza Iridium IX set specifies 2004–2014 2.5L H4 models.

Consider this set only if the CR9EIX name and 10mm thread match the specification you need. It offers four NGK iridium plugs, but the available details do not establish EJ25 fitment.

Listed on Amazon as: NGK CR9EIX – Iridium IX Spark Plug – 4-Pack/–